A major task in the development of advanced drug formulations deals with the elaboration of delivering systems providing sustained release of bioactive materials. Mostly, these delivering systems comprise polymer particles in the size range of 0.1-100 μm. The drug molecules are embedded in polymer matrices or in core-shell structures. In the latter the shell degradation rate determines the release rate of the bioactive core material.
Recently, a novel type of shell structure constituting polymer capsules has been introduced. These novel hollow polymeric capsules have a predetermined size in the sub-micron and micron range and tunable wall properties. These capsules are fabricated by means of layer-by-layer (LbL) assembling of polyelectrolytes onto colloidal particles with subsequent removal of the colloidal core. The layer-by-layer (LbL) assembling is performed by alternating adsorption of oppositely charged species, such as polyelectrolytes onto the surface of colloidal particles. The driving force for LbL adsorption is the electrostatic attraction between the incoming polymer and the surface. It was established that the capsule walls have semipermeable properties. They are permeable for small molecules such as dyes and ions while they exclude compounds with a higher molecular weight.
State of the art also includes systems having controllable or adjustable loading as well as release properties, which allows the loading or release of materials into and from capsules by modifying the capsule wall permeability via variations in environmental conditions.
Lab-on-a-chip (LOC) concept is now widely applicable to chemical and biological detection, analysis and reaction. Current state of the art involves immobilization of host molecule(s) onto a substrate in a predetermined pattern, where patterned and functionalized colloidal particles used greatly enhances the detection efficiency and sensitivity.